Methods and apparatus for synthesizing a variety of different types of polymers are well known in the art. For example, the "Merrifield" method, described in Atherton et al., "Solid Phase Peptide Synthesis," IRL Press, 1989, which is incorporated herein by reference for all purposes, has been used to synthesize peptides on a solid support.
Methods have also been developed for producing large arrays of polymer sequences on solid substrates. These large "arrays" of polymer sequences have wide ranging applications and are of substantial importance to the pharmaceutical, biotechnology and medical industries. For example, the arrays may be used in screening large numbers of molecules for biological activity, e.g., receptor binding capability. Alternatively, arrays of nucleic acid probes can be used to identify mutations in known sequences. Of particular note, is the pioneering work described in U.S. Pat. No. 5,445,934 (Fodor et al.) and U.S. Pat. No. 5,510,270 (Fodor et al.) which disclose improved methods of molecular synthesis using light directed techniques.